The propposed work involves a study of the immunogenicity of Plasmodium berghei antigens derived from asexual erythrocytic parasites cultivated in vitro. Although culture methods to date are not supportive of parasite invasion at frequencies permitting continuous culture, data from the applicant's laboratory indicate that intracellular parasite development proceeds normally to schizogony and merozoite release. Studies are planned to define the time-course of development of functionally protective antigens on the parasite as development proceeds in vitro, after initiating culture with schizont-depleted populations of parasites. The possible inhibitory role played by non-merozoite antigens is under study, and the immunization trials are accompanied by polyacrilamide gel electrophoretic analysis of the parasite proteins.